Basic Human Nutrition
Lecture 7
Healthy Weights, BMI, Physical
Activity Recommendations
Body Weight
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Body composition is the proportion of muscle,
bone, fat and other tissues that make up
body weight.
Achieving and maintaining a healthy weight is
about managing energy balance and
increasing the proportion of lean to fat tissue.
Energy balance = energy in – energy out.
Energy balance
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Energy in = calories consumed per day.
Energy out = basal metabolic rate
(BMR) + thermic effect of foods, +
physical activity per day.
Small increments in calories consumed
per day or week can contribute to
weight gain over time.
Energy in
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1 pound of pure fat = 9 x 450g = 4,050
calories;
Body fat consists of water, fat and protein =
3,500 calories.
Calories in foods are obtained by measuring
the heat energy released when foods are
burned in a bomb calorimeter.
Food composition tables or data bases
publish caloric content of commonly eaten
foods.
What makes us eat?
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Hunger: physiological need to eat
Appetite initiates eating. It is a desire
to eat that accompanies sight, smell or
thought of appealing foods.
Appetite is learned behaviour.
What makes us stop eating?
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Satiation: the perception of fullness
that gradually builds throughout a meal.
When the stomach stretches, chemical
messengers are sent to the brain to
indicate fullness.
The brain releases neurotransmitters that
suppress food intake in response.
Satiation occurs, the persons feels full and
stops eating.
Satiety
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Satiety continues to suppress hunger
for several hours. Satiety determines
the length of time between meals.
Satiation tells the body when to stop
eating, satiety allows the body to stay
stopped for awhile.
Leptin, a hormone produced by the
adipose tissue, controls satiety.
Satiety continued
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Protein foods most satiating
CHO next especially if high in fibre
Foods high in fat have low satiety.
Overriding satiety and satiation cues leads to
overeating.
Energy out
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Thermic effect of food-estimated at
10% of total energy intake
Basal Metabolic Rate (BMR) is the
rate at which the body uses energy to
support its basal metabolism.
Physical activity
Thermic effect of food
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Specific dynamic effect of food –
estimated energy used in digestion and
absorption of food.
Diet induced thermogenesis is  energy
due to  in metabolic rate due to overeating
 CHO 5-10%
 Fat 0-5%,
 Protein 20-30%
 Alcohol 20%
BMR
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Basal metabolic energy required to support
the basic processes of life, including
circulation, respiration, temperature
maintenance, etc. It excludes digestion and
voluntary activities.
BMR constitutes the largest proportion (2/3)
of a person’s daily expenditure.
Factors that affect BMR
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Age – BMR higher in youth. Lean body
mass declines with age; physical activity
can offset this effect.
Height – tall people have larger surface
area.
Growth – children & pregnant women
have higher BMR’s
BMR continued
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Body composition – more lean tissue, higher
BMR
Fever – raises BMR
Stress
Environmental temperature
Fasting/starvation, lowers BMR
Malnutrition, lowers BMR
Thyroxine – regulates BMR
Physical activity and energy
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Most variable and changeable
Voluntary
It can be significant in weight loss and
weight gain
Duration, frequency and intensity
influence energy expenditure.
Energy Needs
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Energy needs in tables are based on
average people
Men have more metabolically active
tissue (muscle) than women.
Caloric needs = BMR + energy needed
to fuel voluntary activities (walking,
sitting, skiing, swimming, etc.).
Estimating energy (caloric)
needs
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To calculate energy needs:
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BMR factor of 1.0/kg body weight per hour
for men
0.9/kg body weight/hr – women
Multiply weight in kgs by BMR factor.
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E.g., 68 kgs x 1 = 68 cals/hr
Multiply calories/hr x hrs in a day = 68 x
24 = 1,632 calories per day.
Classification of physical
activity
Sedentary
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Women 25 – 35%
Men 25 –40%
Light Activity
Men 50 – 70 %
Women 40 – 60%
Moderate Activity
Men 65 –80%
Women 50 – 70 %
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Sit down most of day,
drive or ride whenever
possible.
Move around some of
the time, standing,
walking occasionally
Engage in some
exercise, 1 hr of jogging
4 –5 times /week or
occupation calls for
some physical work
Classification of activity
continued
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Heavy Activity
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Men 90 – 120 %
Women 80 – 100%
Exceptional
Activity
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Men 130 –145 %
Women 110 – 130 %
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Job requires much
physical labour, e.g,
roofer, carpenter
Intense physical
activity for hours professional or
college athletes
during training
seasons
Calculating Calorie needs
continued
Estimate physical activity expenditure.
• Male Student, bikes 10 mins/day, walks to
classes, otherwise sits and studies.
• Student in Light Activity, 50% - 70%
• 1,632 cals /day x 0.50 = 816 cals/day
• 1,632 cals/day x 0.70 = 1,142 cals/day
• Add BMR + each of above values = range
of 2,448 to 2774 or 2500 to 2800 cals per
day.
Defining a healthy body weight
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Fashion trends
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Health
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Society values change over time
Perceived body images
Good health supercedes appearance
Longevity
Body Mass Index (BMI) measures
relative weight for height
BMI
Values
Used to
Assess
Weight
Measuring weight & body fat
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Weight for height tables
Body Mass Index (BMI) weight in kgs
divided by height in metres squared
Waist to hip ratio/ waist circumference
Anthropometric measures – skinfold
tests
Bioelectrical impedance
Underwater weighing
Estimating body fatness
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Anthropometry: skinfold measurements and
waist circumference.
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Skinfold test measures level of fat under skin at
several places: triceps muscle, subscapular,
suprailiac and back of the thigh. Measurements
are added and compared to a standardized chart
for men and women.
Waist measurement done with tape measure. Men
102 cm (40”) Women 88 cm (35”). Measure of
visceral fatness and distribution of fat at abdomen.
Estimating body fatness
continued
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Underwater weighing – measures body
density and volume. Lean tissue is denser
than fat tissue, so the denser a person’s body
is the more lean tissue it contains.
Bioelectrical impedance measures how a
small, harmless electrical charge is conducted
through the lean tissue of the body and
reflects the body’s contents of lean tissue and
water.
Estimating body fat continued
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Combination of non-invasive measures of BMI
with waist circumference gives a good overall
estimate of body fat for most of the adult
population under 65.
Average body fat for men is 15% of body
weight and 20% for women.
Obesity when body fat exceeds 22% in young
men, 25% in older men; 32% in younger
women and 35% in older women. Age 40
dividing line between younger and older.
Methods Used to
Assess Body Fat
Body fat distribution
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Fat needed for fuel, insulation and
protection of organs
Fat assists in nerve impulse
transmission
Fat supports normal hormone activity
Fat distribution –abdominal –central
obesity- increases health risks
apple versus pear shape
Risks of being underweight
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Inadequate fat stores to support life in
event of famine or illness.
Low blood pressure
Susceptibility to cold
Anaemia in women
Risks of being overweight
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Increased risk of:
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Cardiovascular disease
High blood pressure
Diabetes
Osteoarthritis
Sleep apnea
Gout, gallbladder disease, varicose veins
Abdominal hernias, complications in surgery and
pregnancy.
BMI: health risk for diabetes,
hypertension, heart disease
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<18.5 Underweight
18.5 – 24.9 Normal
25. – 29.9 overweight
30 – 34.9 class I obesity
35. – 39.9 class II
obesity
40 or above class III
obesity
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Lower BMI, greater risk
to health
Very low risk
Increased risk/high risk
High risk/very high risk
Very high risk
Extreme risk
Overweight versus overfat
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BMI not suitable for athletes. Muscle
weights more than fat, therefore may
be classified as overweight but have
lots of muscle not fat.
Pregnant & lactating women
Adults over 65, (shrink with age)
Can you be over-fat and
healthy?
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Yes, if you are fit.
Physical fitness improves cardiovascular
health –circulation and blood lipids; lowers
blood sugar, decreases hypertension and
strengthens muscles including the heart.
Cardiovascular fitness may be more important
than body weight in maintaining health.
Why do people get fat?
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Overeating
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Availability of food
Eating out
Portion distortion
Physical inactivity
Genetics
Preference for high-fat foods
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Fat delivers 2 x the calories of protein or CHO
Fat is stored preferentially by the body and
with great efficiency
Of the 3 energy nutrients, fat stimulates the
least energy expenditure in diet
thermogenesis.
Of the 3 energy nutrients, fat is the least
satiating thus leading to over-consumption.
Physical inactivity
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Overweight people spend more energy in
daily activities than normal weight people,
however, engage in less physical activity.
Physical activity burns calories, builds lean
tissue which is more metabolically active so
assists with weight loss.
One study found that TV watching increases
obesity in children by 2% per hour of
watching TV per day.
One study found that watching TV expends
less energy than doing nothing!
Genetic causes
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Genetics affect tendency to obesity.
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1 parent overweight -60% chance of offspring
becoming overweight.
2 parents overweight – 90% chance for offspring
Supported by studies on twins raised apart, &
adopted children who weigh similar to biological
parents.
Genetic factors
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Leptin –protein that acts as hormone to
increase energy expenditure and
decrease appetite.
Ghrelin – protein that acts like hormone
to decrease energy expenditure and
increase appetite
Uncoupling proteins –white fat/brown
fat
Leptin
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Leptin suppresses neurotransmitter
NPY, the strongest appetite stimulator
in the brain.
Injections of leptin to reduce obesity?
No. Most obese people already have
high levels of leptin, only a very few do
not produce leptin.
Leptin continued
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As body fat increases and leptin increases,
the brain’s receptors may become less
receptive to leptin
Leptin has other roles: e.g., may inform the
female reproductive system about fat
reserves, stimulates growth of new blood
vessels, acts on bone marrow cells to
enhance their maturation into specialized
cells, etc. Therefore, cannot inject leptin
freely.
Proposed theories for obesity
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Set point theory
Fat cell number theory
Enzyme theory
External cue theory
Set-point theory
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The theory that the body tends to maintain a
certain weight by means of its own internal
controls. Appetite and satiety regulators are
manipulated by the body to maintain a
specific weight.
Enzyme theory: LPL or lipoprotein lipase
enables fat cells to store triglycerides.
Concentrations of LPL increase as fat cells
become enlarged with fat.
Fat cell number theory
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Excess fat cells acquired in childhood. Obesity
depends on number and size of fat cells.
Obese children entering teen years may have
as many fat cells as normal weight adults.
Fat cells of obese people contain more LPL,
therefore more efficient at storing fat.
May explain why obese people have problems
losing and maintaining weight loss.
Behavioural causes of obesity
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External cue theory: people override signals
of satiety and hunger when presented with
circumstances that stimulate them to do so.
E.g., going into a chocolate shop; friend
offering bag of chips. People eat even though
not hungry.
Stress can trigger over-eating
Poor self-esteem can trigger over-eating
Social Consequences of obesity
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Prejudices and discrimination
Judged on appearance rather than
character or ability
Stereotyped as lazy and lacking selfcontrol
Psychological Problems
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Feelings of rejection, shame and
depression are common
Search for ineffective treatments with a
sense of failure
The
Psychology
of Weight
Cycling
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Dangerous interventions
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Fad diets
Drugs
Herbal products and dietary
supplements
Surgery
How does the body lose weight?
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Restricting calories results in body’s use of
stored fuel.
With moderate restriction, adequate protein
and CHO, body uses stored fat and slow,
gradual weight loss occurs.
Fasting requires the body to 1) use up body
glycogen stores, 2) draw on lean tissues to
convert protein to glucose to maintain the
body’s systems and 3) convert fat into
ketones.
Ketone bodies
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Are acidic compounds derived from fat
and certain amino acids that can be
used by the brain for energy when CHO
not available.
After about 10 days, the brain and
nervous system can meet most of their
energy needs from ketones.
Ketones are toxic to system and must
be removed in the urine.
Fasting versus moderate weight
loss
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In fasting, the body’s lean tissues continue to
be degraded. The body is deprived of
nutrients it needs to make new enzymes, red
and white blood cells and other vital
components. Energy metabolism is slowed.
Moderate energy restriction, promotes
greater weight loss, faster rate of fat loss,
and protects lean tissues and metabolic rate
than a severely restricted fast.
Low CHO diets
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Common names:
Atkins New Diet Revolution, Calories
Don’t Count, Drinking Man’s Diet, Mayo
Diet, Protein –Sparring Fast, Scarsdale
Diet, Ski Team Diet, Stillman Diet, and
Zone Diet.
CHO diets
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Bring about responses similar to fasting
Ketones suppress appetite, therefore,
weight loss occurs because of restricted
calorie intake due to loss of appetite,
monotony of diet, and large fluid losses.
Weight is regained at a rapid rate.
Side effects of low CHO diet
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Nausea
Fatigue
Constipation or diarrhea
Low blood pressure
Elevated uric acid (gout)
Foul taste in the mouth
Bad breath
Dangerous
Interventions
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Herbal products and dietary
supplements
 Ephedra
 Ma Huang
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Aggressive Treatments
Of Obesity
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Clinically severe obesity
Drugs
 Sibutramine –suppresses
appetite, many side effects
 Orlistat- blocks fat digestion and
absorption –many side effects
 Both need low-cal diet & exercise
to be effective.
Surgical interventions
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Gastric surgery used in severely obese
Has short-term and long-term
complications
Requires adherence to low-cal diet and
very small amounts of food
Surgical Procedures
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Achieving and maintaining a
healthy body weight
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Do not restrict calories below 1200 for
women and 1500 for men. If very overweight
maintain higher calorie level, eg., 1800 cals
for women and 2000 for men.
Diet based on CFGHE, with lots of variety to
meet nutrient needs. Minimum servings per
group provide about 1800 cals/day.
High in fibre and moderate in protein 15 –
20% of calories to increase satiety, 20-35%
calories from fat and 45 - 55% from CHO.
Diet strategies that work
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Set realistic goals for weight loss. Aim for
weight loss of 1 to 2 lbs per week.
Start with staged goals, i.e., lose 10 pounds
in 6 weeks. Continue until reach goal weight.
Identify Cues which trigger emotional eating,
and over-eating. Identify solutions to deal
with them.
Modify environment and/or behaviour to
avoid foods or situations that trigger overeating.
Weight-Loss Strategies
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Reasonable goals vs. expectations
Copyright 2005 Wadsworth Group, a division of Thomson Learning
Change behaviours
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Eat regular meals and low-fat snacks
Drink water instead of high calorie
beverages
Eat slowly
Plan meals away from home
Keep records of foods and beverages
eaten. Helps to keep people on tract.
Avoid sabotage …
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Get support from family, friends and coworkers
Never punish yourself for “slipping” and
ask that friends make no comment on
your “slipped” behaviour.
Reward yourself with non-food rewards
for successfully attaining goals.
Increase physical activity
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Be physically active 30 – 60 minutes on
most days of the week.
Timing does not matter
Low-to moderate intensity for long
periods recommended
Choose activities that you enjoy and are
willing to do regularly.
Benefits of physical activity
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Increases lean tissue (muscle) and
reduces body fat.
Increases metabolism-lose weight faster
Exercise may help decrease appetite
Reduces stress
Increases energy
Psychological benefits: look better, feel
better
Reliable nutrition websites
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www.hc-sc.gc.ca/nutrition/resources.htm
www.dietitians.ca/eatwell
www.eatright.org
US National Heart Lung and Blood Institute
NHLBINetwork@AIR.org
(Portion Distortion Quiz)
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www.webmd.com - description and
evaluation of many common diets